The present invention relates to diffractive light modulators. More particularly, this invention relates to diffractive light modulators with dynamically rotatable diffraction planes.
Bloom et al. in U.S. Pat. No. 5,311,360, entitled xe2x80x9cMethod and Apparatus for Modulating a Light Bean,xe2x80x9d teach a grating light valve which operates in a reflection mode and a diffraction mode. The grating light valve includes elongated elements suspended above a substrate. In the reflective mode, reflective surfaces of the grating light valve cause incident light to constructively combine to form reflected light. In the diffractive mode, the reflective surfaces of the grating light valve are separated by about a quarter wavelength of the incident light to produce diffracted light. When the grating light valve is in the diffractive mode, the grating light valve predominantly diffracts light into a plus one diffraction order and a minus one diffraction order but also diffracts a small amount of light into higher diffraction orders. The incident light diffracts according to the direction of periodicity. In the case of the grating light valve, the direction of the periodicity is perpendicular to the elongated elements. Therefore, in the diffraction mode, the light is diffracted in a diffraction plane perpendicular to the elongated elements.
In WDM (wavelength division multiplex) optical communication, multiple component wavelengths of light each carry a communication signal. Each of the multiple component wavelengths of light form a WDM channel. Many applications require switching of a signal from one channel to another. Other applications require the equalization of the output signals as well as excellent extinction in the non-switched fibers. For example, switching an input light signal from one channel to another can be achieved by using a diffractive light modulator, such as a grating light valve, to diffract the input light into a first order of light, while reflecting very little light, ideally no light, as specularly reflected zero order light. The diffracted light is diffracted along a known diffraction plane and the first order light is collected as output for an output port of a switch. The diffracted first order light can also be attenuated by controlled means, thereby equalizing the light that has been xe2x80x9cswitchedxe2x80x9d into the first order. It is common practice to perform the switching and equalizing functions at the same physical location for convenience, maintenance, and economic advantages.
Although light can be diffracted into higher orders than the first order for switching and attenuation applications, it is easier and more efficient to diffract and collect light into and out of the first order. However, not much flexibility is provided with only one first order per diffraction plane.
What is needed is a diffractive light modulator that produces multiple diffraction planes. What is further needed is a diffractive light modulator that produces multiple diffraction planes and dynamically utilizes the multiple diffraction planes.
An embodiment of the present invention includes a light modulator. The light modulator includes elongated elements and a support structure. The elongated elements are arranged in parallel. Each element includes a light reflective planar surface with the light reflective planar surfaces lying in one or more parallel planes. The support structure is coupled to the elongated elements to maintain a position of the elongated elements relative to each other and to enable movement of each elongated element between a first modulator configuration and a second modulator configuration. In the first modulator configuration, the elongated elements act to reflect incident light as a plane mirror. In the second modulator configuration, selected groups of elements are deflected and act to diffract the incident light along one or more of a plurality of diffraction planes. The groups of elements are configured according to one of a plurality of selectable group configurations. Each group configuration corresponds to one of the plurality of diffraction planes.
Each element includes a first edge and a second edge. In an active optical area, the first edge is preferably linear and is formed at a first edge angle relative to a lengthwise axis of the elongated element. The second edge is also preferably linear within the active optical area and is formed at a second edge angle relative to the lengthwise axis of the elongated element. The first edge angle is preferably zero and the second edge angle is preferably non-zero. Each group configuration includes at least two adjacent elements such that one of the first edge and the second edge of a first end element of the group configuration forms a first outer group edge, and one of the first edge and the second edge of a second end element of the group configuration forms a second outer group edge. The edge angles of the first and second outer group edges are the same. Alternating groups of elements can be deflected a distance of about one-quarter the wavelength of the incident light thereby diffracting the incident light along a first diffraction plane perpendicular to the outer group edge. One or more elements of each group of a remaining groups of elements can be deflected a distance within a range of zero to about one-quarter the wavelength of the incident light, thereby diffracting a portion of the incident light along a second diffraction plane perpendicular to a non-deflected element edge nearest the one or more elements. A selectable diffraction plane is formed perpendicular to the outer group edge of each group configuration.